This invention relates in general to a vehicle suspension assembly and in particular to a front axle and steering gear assembly preferably for use in a commercial vehicle suspension assembly.
A commercial vehicle, as described herein, is typically a heavy vehicle such as a truck or bus, as well as similar freight and utility vehicles. Such vehicles are typically known as Class 2 (or higher) vehicles and such classification is based on Gross Vehicle Weight (GVW). Vehicles can be rigid (e.g. a truck) or combination (e.g. a truck and trailer). The GVW of a vehicle is the gross laden weight (GLW) or gross combined weight (GCW) if it's a combination vehicle. The Gross Vehicle Weight (GVW) means the weight of a fixed or combination vehicle, together with any load it is carrying (including equipment and accessories). Such vehicles typically, according to conventional technology, incorporate a longitudinal chassis element in the form of two side frame members which are connected to one another by a number of cross-members. The side frame members extend substantially parallel with one another along substantially the whole length of the vehicle and support vehicle components such as the engine, the driver's cab and a load surface which takes the form of, for example, a load platform or a superstructure. In addition, the vehicle's front and rear axles are suspended from the frame side members.
In heavy vehicles, the side frame members and the cross-members act as the main load bearing elements of the vehicle in order to provide strength and rigidity thereto. In heavy vehicles, the body work also contributes to vehicle rigidity and strength. Conventionally designed support devices are nevertheless built so as to allow slight bending and torsion in order to be able to cope with heavy loads and varying road conditions. Relatively low resistance to bending and torsion does entail, however, certain problems with regard to riding comfort and vehicle running characteristics. The use of a chassis element having relatively low resistance to torsion (and the wheel axles being made of steel) can result in unsatisfactory riding comfort. Riding comfort is an increasingly important factor due to the number of heavy vehicles that are travelling on smooth roads as well as in off-road conditions. In addition to riding comfort being important for the vehicle's driver and passengers, it is also important to reduce the amount of damage to freight, particularly when carrying goods which are easily damaged. Conventional frame side members and steel wheel axles result in any road surface unevenness being propagated in the support device and having adverse effects on substantially the whole vehicle.
The conventional structure of a heavy vehicle also has the disadvantage that its manufacture is relatively expensive because such a design involves many different components which cannot be standardized for different vehicle variants. For example, the vehicle's front and rear axle arrangements may involve many different components depending on whether the respective wheels are to be steerable or not, powered or not, how many rear axles the vehicle is to have, the type of suspension, etc. Such a conventionally constructed heavy vehicle also requires a relatively large amount of assembly work.
To operate the steering of such a heavy vehicle, the vehicles typically include a re-circulating ball steering assembly. Re-circulating ball steering assemblies typically includes linkages that turn the vehicle wheels in a manner that is different than with a rack and pinion system. Most re-circulating ball steering gears include a worm gear. The worm gear comprises two parts, a block with a threaded opening with gear teeth on an outer surface thereof that engages a gear that moves a pitman arm. The steering wheel connects to a threaded rod, similar to a bolt, that fits into the threaded opening of the block. When the steering wheel turns, it turns the bolt. The bolt is held fixed so that when it spins, it moves the block, which in turn moves the gear that turns the wheels. Instead of the bolt directly engaging the threads of the block, all of the threads are filled with ball bearings that re-circulate through the gear as it turns. The balls, therefore serve two purposes. First, they reduce friction and wear in the gear, and second, they reduce chucking motion or play within the gear. The play or chucking would be felt when the steering wheel direction is changed. Without the use of the balls, the teeth would come out of contact with each other for a moment, thereby making the steering wheel feel loose.